All routers I have show all devices they have dealt with in the arp table. Localnet traffic may not go through the router, so if the device never contacts the router with an WAN (non-localnet) request, it is possible the device mac address may not end up in the arp table. I have the ability to ping from my router. That almost guarantees an entry in the arp table.

What is your concern about the mac address? If you want to know if it is assigning the correct mac address from the SD, then Serial.print() the mac address when you get it from the SD card before assigning it to the w5100.

edit: If you use dhcp to get an ip, you should be able to find the mac address in the dhcp lease records in the router.

Here is a post that shows my code for using the SD card to store network settings.http://arduino.cc/forum/index.php/topic,128763.msg976118.html#msg976118

All routers I have show all devices they have dealt with in the arp table. Localnet traffic may not go through the router, so if the device never contacts the router with an WAN (non-localnet) request, it is possible the device mac address may not end up in the arp table. I have the ability to ping from my router. That almost guarantees an entry in the arp table.

What is your concern about the mac address? If you want to know if it is assigning the correct mac address from the SD, then Serial.print() the mac address when you get it from the SD card before assigning it to the w5100.

edit: If you use dhcp to get an ip, you should be able to find the mac address in the dhcp lease records in the router.

Here is a post that shows my code for using the SD card to store network settings.http://arduino.cc/forum/index.php/topic,128763.msg976118.html#msg976118